Workshop on Frontiers in Ultrafast Scattering of Electrons

Aug 27, 2025, 8:00 AM → Aug 29, 2025, 5:30 PM America/Los_Angeles

48/1-112A/B/C/D - Redwood Rooms (SLAC)

Alexander Reid (SLAC), Joel England (SLAC)

We are pleased to announce the first workshop on Frontiers in Ultrafast Scattering of Electrons (FUSE), to be held August 27-29, 2025 at SLAC National Accelerator Laboratory in Menlo Park, California. The workshop aims to enhance the visibility of relativistic electron scattering as a critical research tool, foster collaboration across the broader ultrafast electron diffraction (UED) community (including both relativistic and nonrelativistic UED instruments), and serve as a platform for practitioners to exchange ideas, share breakthroughs, and address emerging challenges. The workshop is open to the global UED science and instrument development community to attend. We will arrange invited talks from international leaders, particularly those from regions with significant UED investments, to relate recent scientific developments, share capabilities and progress from emerging UED facilities, and identify opportunities for innovation. An auxilliary goal is to inform SLAC’s MeV-UED program so that it will remain user-driven while adapting to evolving trends in ultrafast science. Such engagement will be vital for maintaining the value of MeV-UED as a research tool and maximizing its scientific impact. 

 

Made possible with generous support from the following sponsors:

 

 

 

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Wed, August 27

8:00 AM Coffee Break

Welcoming Remarks

Convener: Joel England (SLAC)

1 Welcoming Remarks

Speaker: Alexander Reid (SLAC)

2 Historical Perspectives and Outlook for MeV-UED

Speaker: Pietro Musumeci (UCLA)

MeVUED_SLACAug25_Musumeci_RD.pdf

3 Logistics and Workshop Charge

Speaker: Joel England (SLAC)

FUSE_Welcome.pdf

9:30 AM Coffee Break

UED Facilities

Opening remarks

Convener: Stephen Weathersby (SLAC)

4 3D atomic structure determination with MeV electron diffraction

For UED experiments DESY operates the ‘relativistic gun for atomic exploration (REGAE)’. REGAE generates electron pulses with an energy of 2 - 5 MeV and a charge of up to 100 fC. An additional buncher cavity allows compress these pulses to 20 fs. For diffraction experiments with solid state samples, REGAE is equipped with a crystallography goniometer and a Jungfrau 1M detector, which allowed us to perform first high quality 3D structure determinations of inorganic samples. In the next step we plan to extend these measurements to the time-domain. In parallel, we are working on the implementation micro-beam bunch train mode for measurements of biological samples.

Speaker: Alke Meents

UED_workshop_2025_08_3d_structure_determination.pdf

5 The Future RUEDI (The Relativistic Ultrafast Electron Diffraction and Imaging) UK facility

Speaker: Julian McKenzie

2025,08,27 RUEDI JWM SLAC FUSE Workshop.pdf

6 MeV UED facility at SJTU

Abstract: The National Science Foundation of China supported the construction of a MeV UED/UEM facility at Shanghai Jiao Tong University from 2014 to 2019. The facility achieved a high temporal resolution of <50 fs (FWHM) and supported about 20 experiments since 2020. I will discuss the critical technologies that enabled the high temporal resolution.

Speaker: Dao Xiang (SJTU)

7 KAERI MeV-UED: Setup and Applications to Ultrafast Chemical Dynamics

The MeV-UED facility at the Korea Atomic Energy Research Institute (KAERI) has been
constructed to investigate ultrafast structural dynamics with a focus on experimental flexibility.
This talk will provide an overview of the beamline configuration and timing system, followed
by a detailed look at the experimental setup, including gas sample delivery system, interaction
chambers, and environmental controls tailored for time-resolved chemical studies. While the
system is still under development for broader user access, early experiments have demonstrated
the platform’s applicability to real-time molecular dynamics. We aim to share our
implementation experience and engage in practical discussions on system integration and
operation across the UED community

Speaker: Jun Heo (KAERI)

2025_08_27_Jun_Heo_FUSE.pdf

8 SLAC MeV-UED R&D Upgrade Plans

Speaker: Joel England (SLAC)

FUSE_England_2025_RD.pdf

12:30 PM Lunch (Provided)

MeV-UED Enabled Ultrafast Chemical Science in Gas and Liquid Phases

Gas and Liquid Phase Chemical Science Enabled by MeV-UED

Convener: Yusong Liu (SLAC)

9 Speaker Introductions and Session Overview

Provide an introduction to the invited speakers and an overview of the scientific presentations in the session.

Speaker: Dr Yusong Liu (SLAC, LCLS)

FUSE_2025_ChemicalScience_Workshop_27_afternoon_introduction.pdf

10 Gas-phase Ultrafast Electron Diffraction: Achievements, challenges and opportunities

Gas-phase ultrafast electron diffraction (UED) has become a powerful tool for capturing molecular dynamics with femtosecond temporal and atomic spatial resolutions, enabling direct observation of phenomena such as photo-dissociation, ring-opening reactions, and nuclear wavepacket motion through conical intersections. Despite significant progress, several challenges remain: temporal resolution is limited by space-charge-induced pulse broadening; background signal subtraction is complex; structural retrieval methods lack standardization and are error-prone in low-signal regimes; and stable delivery of gas-phase samples with sufficient density is technically demanding. Advances in relativistic electron sources, pulse compression, electron counting detectors, and novel data analysis methods are rapidly expanding the capabilities of gas-phase UED, enabling studies of increasingly complex systems. This talk will provide an overview of the current capabilities, highlight persistent technical challenges, and explore future directions for UED within the broader context of ultrafast science.

Speaker: Dr Pedro Nunes (Diamond Light Source, Ltd)

11 Studying the UV-induced isomerization and dissociation dynamics of gas-phase oxazole and isoxazole

The five-member ring isomers oxazole and isoxazole (C3H3NO) are an interesting model system for studying UV-induced isomerization and dissociation since the different types of bonds in both isomers (C-N-C-O vs C-N-O-C) are predicted to lead to very different reaction products and dynamics. I will present time-resolved product yields for both isomers obtained from a recent GUED experiment and compare the experimental findings to results of trajectory surface hopping simulations as well as time-resolved Coulomb explosion imaging experiments performed at Kansas State University.

Speaker: Prof. Daniel Rolles (Kansas State University)

12 UED Studies of the UV Photochemistry of Isolated and Solvated Bromoform

Bromoform (CHBr3) is a natural compound whose UV photodissociation products contribute to ozone depletion in the Earth’s atmosphere. Ultrafast electron diffraction is used to study atomic rearrangements in isolated and in solvated bromoform molecules after 267 nm excitation. The gas phase study provides the first experimental visualization of a long-predicted ultrafast isomerization channel. The rate-of-formation, lifetime, and predominant yield, relative to a previously observed direct dissociation channel, challenge state-of-the-art theories (JACS 2024, 146, 28070, DOI: 10.1021/jacs.4c07165). More recently, a liquid phase UED study has been performed on bromoform solvated in 1-propanol to test and refine previously reported, solvent-mediated UV reaction mechanisms. Parallels and differences between the observed gas- and solution-phase dynamics will be discussed.

Speaker: Dr Oliver Gessner (LBNL)

3:35 PM Coffee Break

13 Capturing Chemical Motion in Solution: Insights from Femtosecond X-ray and Electron Scattering

Femtosecond X-ray solution scattering (XSS) has enabled us to capture photoinduced structural dynamics in solvated transition metal complexes with atomic-scale resolution, revealing intramolecular changes, vibrational coherences, and solvation dynamics. In this talk, I will present recent XSS results from the LCLS, with a particular emphasis on tracking photoinduced solute–solvent hydrogen-bond rearrangements coupled to ultrafast electron transfer (Nature Chem. 13, 343–349, 2021). I will also discuss opportunities for probing chemical dynamics in solution using ultrafast electron diffraction (UED), highlighting insights from the photodissociation of tri-iodide studied at the LCLS MeV-UED instrument (Struct. Dyn. 7, 064901, 2020).

Speaker: Dr Elisa Biasin

FUSE_EBiasin.pdf

14 Laser-Induced Streaking in Liquid-Phase Ultrafast Electron Diffraction

Laser-induced streaking (LIS) of electron beam, first observed by Zewail group back in 1994, is a unique phenomenon in UED that is often used to conveniently identify time-zero in UED experiments. In the gas phase, LIS originates from plasma field created by strong field ionization of sample molecules, hence named as “photoionization-induced lensing” by Zewail. Separately, LIS can also be achieved with THz pulses, known as the THz streaking. THz streaking do not involve photoionization, but originates from the amplification of the electric field of THz pulses by a metal cavity. In this presentation, I will show our preliminary results on LIS in liquid-phase UED. We found that in liquid-phase, LIS can originate from a third mechanism that is different from the two mechanisms above. In addition to the main beam, liquid-phase LIS also streaks the diffraction pattern. This phenomenon creates both complexity and new opportunity for future liquid-phase UED experiments.

Speaker: Prof. Jie Yang (TsingHua University)

Thu, August 28

8:00 AM Coffee Break

Solid State & Quantum Materials

Convener: Alexander Reid (SLAC)

15 Structural contribution to light-induced gap suppression in Ta2NiSe5

An excitonic insulator is a material that hosts an exotic ground state, where an energy gap opens due to spontaneous condensation of bound electron-hole pairs. Ta2NiSe5 is a promising candidate for this type of material, but the coexistence of a structural phase transition with the gap opening has led to a long-standing debate regarding the origin of the insulating gap. In this talk, I will discuss our recent effort in using ultrafast electron diffraction to obtain quantitative insights into the atomic displacements in Ta2NiSe5 following photoexcitation, which has been overlooked in previous time-resolved spectroscopy studies. In conjunction with first-principles calculations using the measured atomic displacements, we find that the structural change can largely account for the photoinduced reduction in the energy gap without considering excitonic effects. Our work illustrates the importance of a quantitative reconstruction of individual atomic pathways during nonequilibrium phase transitions, paving the way for a mechanistic understanding of a diverse array of phase transitions in correlated materials where lattice dynamics can play a pivotal role.

Speaker: Alfred Zong (Stanford)

16 X-ray diffuse scattering studies of structural dynamics in quantum materials

Speaker: Mariano Trigo (SLAC)

17 Visualizing Energy Transfer and Phonons During Charge Transfer at 2D van der Waals Heterojunctions Using Ultrafast Electron Diffraction

Van der Waals crystals enable the construction of arbitrary, atomically precise heterostructures through straightforward layering of different monolayers without requiring covalent bonds or epitaxial matching. Understanding charge and energy transfer mechanisms in these atomically thin, two-dimensional (2D) material interfaces is fundamental to their electronic and electrochemical applications. Earlier research has demonstrated that extremely rapid charge transfer at energetically staggered or type II heterojunctions between 2D semiconductors occurs within tens of femtoseconds after photoexcitation. However, energy dissipation during charge transfer and the interaction of charge carriers with lattice vibrational modes remain inadequately characterized.
In this work, we utilize ultrafast electron diffraction to directly observe lattice behavior within individual monolayers of van der Waals heterojunctions and uncover how layer-hybridized electronic states influence energy and charge transport across atomically sharp interfaces. Through examination of Bragg peak intensity changes following photoexcitation, we monitor interlayer energy transfer, while phonon dynamics are analyzed via diffuse scattering measurements. Supported by first-principles theoretical calculations, our results elucidate how lattice dynamics and electronic state hybridization contribute to ultrafast electronic phenomena at 2D van der Waals heterojunctions.
Reference:
A. Sood, J. Haber, A. Raja et al. "Bidirectional phonon emission in two-dimensional heterostructures triggered by ultrafast charge transfer," Nature Nanotechnology 18 (1), 29-35 (2023).

Speaker: Archana Raja (LBNL)

10:30 AM Coffee Break

Electron Sources & Beam Optics

Convener: Fuhao Ji (SLAC)

18 Pushing the limits of Ultrafast Electron Diffraction and Imaging at Tsinghua University

Speaker: Renkai Li (Tsinghua University)

FUSE_lrk_20250828_post.pdf

19 Novel Cathodes for Dark Current Mitigation in LCLS-II Injector Gun

High rep-rate SRF-Linac based XFEL like LCLS-II has a stringent requirement on the limit of the dark current from the injector RF gun. In this talk, we will present our recent work on mitigating the LCLS-II gun dark current by re-designing the photo cathode.  New cathode plugs with ~1mm insertion have been designed, manufactured and commissioned at LCLS-II. They successfully reduce the gun dark from ~uA to ~nA level, and can potentially enable further improvement on the beam emittance.

Speaker: Tianhuan Luo (Lawrence Berkeley National Laboratory)

UED2025_Luo.pdf

20 C-band high-gradient photoinjector R&D at LANL CARIE facility

Two high-gradient 1.6-cell normal-conducting RF photoinjectors at C-band were designed for operation at the Cathodes And Radiofrequency Interaction in Extremes (CARIE) facility at Los Alamos National Laboratory (LANL). The first photoinjector cavity uses a planar copper cathode and has been fabricated and tuned at low power. The second photoinjector cavity was designed for using INFN-style photocathode inserts and is currently under fabrication. The high-power RF system of CARIE comprising a 50-MW 5.712-GHz klystron, circulator, and waveguide line has been conditioned to providing 12 MW with 1-µs pulse length.

Speaker: Haoran Xu (Los Alamos National Laboratory)

LANL-CARIE.pdf

21 Design of the RUEDI ultrafast electron diffraction beamline at Daresbury Laboratory

RUEDI (Relativistic Ultrafast Diffraction and Imaging) is a planned UK national user facility. It has a diffraction beamline optimised for temporal resolution. This beamline uses an S-band normal conducting RF gun followed by a triple bend achromat magnetic compressor which simultaneously compresses the bunch and suppresses the time of arrival jitter to the 10 fs scale. The compressor has variable R56, sextupoles for control of T566 and optics designed to mitigate space charge degradation of the electron beam quality. After the sample the diffraction patterns are magnified onto the detector using flexible variable camera length solenoid optics.

Speaker: Ben Hounsell (STFC UKRI)

FUSE_BRH_Design_of_the_RUEDI_ultrafast_electron_diffraction_beamline_at_Daresbury_Laboratory.pdf

1:00 PM Lunch (Provided)

Supporting Technologies & Diagnostics

Convener: Cameron Duncan (SLAC)

22 Towards programmable XFELs: linking adaptable photoinjector laser shaping to tailored X-ray production

LCLS-II is advancing attosecond X-ray science by optimizing electron beam generation at the photoinjector through tailored UV laser pulses. We introduce a novel method combining IR spectral shaping and dispersion-controlled nonlinear upconversion to produce customizable UV profiles (e.g., flattop, multi-spike). Preliminary LCLS-II experiments confirm these modulations effectively perturb electron bunches downstream. This approach, integrated into a start-to-end simulation framework, paves the way for programmable, application-specific X-ray pulse generation, enabling end-to-end optimization of XFEL performance.

Speaker: Sergio Carbajo (UCLA)

23 Direct electron detectors for robust structural characterization with four-dimensional STEM

Four-dimensional scanning transmission electron microscopy, where the full forward scattering distribution of the electron beam is recorded by a 2D pixelated detector at each position in a scan, provides a wealth (a deluge?) of information about the sample. Detectors with high dynamic range enable quantitative analysis of the diffraction data, and their high speed (10-100k fps) allows us to defeat drift. In this talk I’ll discuss the factors that make a good diffraction detector, demonstrate how they’ve been leveraged for precise nanoscale measurement of strain, orientation, polarization, and fields, and discuss the strategies for managing and analyzing the large volumes of data they produce.

Speaker: Steven Zeltmann (Cornell)

24 Advanced THz structures for accelerator timing diagnostics

Recent advances in THz acceleration have shown promise for manipulation of mega-electron volt scale electron bunches with high efficiency and small footprint. Over the years we have established various new techniques for THz-driven pulse compression and timing diagnostics utilizing single and dual-fed THz compressor structures to enable much shorter electron pulses and simultaneously improve the time-of-arrival (TOA) jitter. This talk will provide an overview of this effort with recent results of THz structures testing, and also novel ideas for THz generation, coupling, and transport toward improved efficiency of THz driven electron diagnostics.

Speaker: Mohamed Othman (SLAC)

FUSE_workshop-Othman2025.pdf

25 Versatile Photoelectron Sources for Ultra-low Intrinsic Emittance Electron Beams

Laser technologies for generating sub-picosecond pulses at different wavelengths have propelled photocathodes to the forefront of electron sources. By leveraging nanofabrication techniques, photocathode research now promises to deliver sources for beams with sub-micron transverse dimensions and sub-nanometer emittances. The techniques for fabricating these sources are versatile, allowing them to be combined with parallel advances in photocathode research. In this talk I will present recent work in fabricating sub-micron photocathodes and
briefly discuss theoretical work motivating further work.

Speaker: Michael Kaemingk (Los Alamos National Laboratory)

Poster Session (Building 53 Lobby)

6:30 PM No-Host Dinner -- Dutch Goose, 3567 Alameda de las Pulgas, Menlo Park, CA

Fri, August 29

8:00 AM Coffee Break

Materials at Extreme Conditions

Convener: Mianzhen Mo (SLAC)

26 Investigating ultrafast structural changes of warm dense matter – connecting atomistic details with transport properties

When driven to extreme temperatures, solid density matter can exhibit properties different than those found at ambient conditions. Measurement of properties, in particular transport properties such as the electrical conductivity, has been possible by heating thin films of material using ultrafast lasers. However, interpretation of experimental results and comparison with theoretical prediction requires knowledge of the atomic arrangement and phase of the material. Here, we use MeV-UED to study the structural evolution of Al heated to extreme temperatures. The Al films show rapid melting on an ~3 ps timescale, with the measurements indicating that the atoms retain a solid-like structure for the first ps after heating. We combine these results with ultrafast conductivity measurements to correlate the change in the lattice structure as the material melts.

Speaker: Prof. Benjamin Ofori-Okai (SLAC)

27 Radiation induced damage in nuclear materials studied with UED and modeling

Experimental study of early damage in nuclear damage has been very challenging due to low quantity and small size of defects. Therefore, being able to reliably validate modelling techniques of primary damage in nuclear materials has not been possible. Recent, advances in UED experiments has made it possible to study the dynamics of the material due to laser excitation. By comparing the signals from damaged and undamaged material it could be possible to evaluate the types of defects and their concentrations experimentally. Moreover, UED experiments can be directly simulated with computer modelling and, therefore makes it possible to validate the models being used.

In this presentation we present the combined experimental and modelling study to assess the damage and its role on the materials response to laser excitation of pristine and He implanted sample.

Speaker: Prof. Artur Tamm (University of Tartu)

2025-08-26_TAMM_redacted.pdf

28 Ultrafast electron-diffraction studies of materials under extreme conditions

Speaker: Dr Mianzhen Mo (SLAC)

10:00 AM Coffee Break

Cross-Cutting UED Science

In this session, we will focus on the applications of using UED, XUV and similar techniques on the in-situ/operando spectroscopy

Convener: Ming-Fu Lin (SLAC)

29 Probing in-operando device dynamics and atomic-scale energy flows with UED

Speaker: Prof. Aditya Sood (Princeton University)

30 Imaging photoexcited carriers and heat transport in nanoscale materials using ultrafast EELS

Speaker: Prof. Scott Cushing (Caltech)

31 (CANCELLED) Evolving UED Capabilities for Materials Research: Advances in In-Situ experiments

11:30- 12:00

Speaker: Dr Sharon Philip (SLAC)

Workshop Closeout

12:30 PM Lunch (On Your Own)

Advisory Board Meeting (Closed Door): Advisory Board Meeting